77 research outputs found
Coulomb Oscillations of Indium-doped ZnO Nanowire Transistors in a Magnetic Field
We report on the observation of Coulomb oscillations from localized quantum
dots superimposed on the normal hopping current in ZnO nanowire transistors.
The Coulomb oscillations can be resolved up to 20 K. Positive anisotropic
magnetoresistance has been observed due to the Lorentz force on the carrier
motion. Magnetic field-induced tunneling barrier transparency results in an
increase of oscillation amplitude with increasing magnetic field. The energy
shift as a function of magnetic field indicates electron wavefunction
modification in the quantum dots.Comment: 16 pages, 6 figure
Unveiling Hidden Physics in the 215-Kelvin Superconducting Calcium Hydride: Temperature, Quantum and Defect Effects
Temperature and quantum effects induce the structural complexity of condensed
hydrogen, and therefore they are expected to impact nontrivially the structures
of clathrate hydrides. Exemplified by clathrate calcium hydride, we show
through ab initio (path-integral) molecular dynamics simulations that these
effects are indeed pivotal at 100-200 GPa. The quantum equation of states
derived at 300 K suggests that the synthesized samples in previous experiments
were berthollide-like CaH, with the stoichiometric defect
increasing smoothly during decompression. The change of composition provides an
explanation for the experimental observation of positive pressure dependence of
superconducting T below 165 GPa. Furthermore, we find significant proton
diffusion in CaH at 150-300 K, with the diffusion coefficient
reaching 10 cm/s. This suggests a coexistence of superconductivity
and proton diffusion in clathrate hydrides. Our findings underline the
importance of temperature, quantum and defect effects to the understandings of
the structure and pertinent physics in high-T superconducting clathrate
hydrides.Comment: 9 pages, 3 figure
The Monte Carlo Simulation of the Electronic Local Properties in the Two-Dimensional Disordered System
AbstractUsing Monte Carlo simulation method, we studied the influence of the disorder, eigenenergy and bandwidth on the localization length in disordered system. The results reveal that electronic states of system exhibited localization phenomena with the increase of degree of disorder and the localization length can be reduced by the increasing of disorder degree. Moreover the incremental range of localization length had a trend to descend with increase of bandwidth
Daya Antibakteri Estrak Kulit Dan Biji Buah Pulasan (Nephelium Mutabile) Terhadap Staphylococcus Aureus Dan Escherichia Coli Secara in Vitro
Traditional medicine from drug crop has more than a pharmacological effect so that its use should be acurate and correct. The mistake in traditional medicine USAge and or drug crop can be dangerous for health. Therefore, it is required a complete scientific information to avoid it. It had been done the research of anti-bacteria activity test from crude extract of ethyl acetate and ethanol from skin and seed of Pulasan to bacterium Staphylococcus aureus and Escherichia coli with dilution method to determine Minimum Inhibitory Concentration (MIC) and Minimum Bakterisidal Concentration (MBC). The biggest MIC and MBC was respectively obtained from ethyl acetate extract that was 0,76 mg/ml, and ethanol extract that was 156,13 mg/ml. In general, skin and fruit seed extract of pulasan (Nephelium mutabile) has bigger resistance ones to bacterium Staphylococcus aureus compared to Escherichia coli
An Integrated Electromechanical Model of the Fixed-Speed Induction Generator for Turbine-Grid Interactions Analysis
An Integrated Electromechanical Model of the Fixed-Speed Induction Generator for Turbine-Grid Interactions Analysis
When wind turbine is connected to the power grid, the turbine-grid interactions restrict its lifespan and produce adverse effects to the grid. Electrical or mechanical oscillations caused by turbine-grid interactions could gradually be weakened or amplified seriously at a certain frequency. This article discusses all types of interactions between a wind turbine and the grid and the influence of the initial operating point, the parallel capacitor, and the series capacitor on the stability of system. Firstly, an integrated dynamic electromechanical model of a single fixed-speed induction generator (FSIG) wind generation system is derived based on the small signal model of each element. Then, a method of stability analysis based on Kharitonov theorem is introduced. Then, the model details the frequency and damping ratio of oscillation mode and classifies those modes' interactions according to participation factors, followed by time domain simulations by the single FSIG generation system to testify the results. Finally, the article studies all the oscillation modes when the initial operating point, the parallel capacitor, or the series capacitor change in the integrated model, which can be verified by Kharitonov polynomials. The indicative findings help to design the damping control to mitigate turbine-grid interactions.</p
An Equivalent Calculation Method for Press-Braking Bending Analysis of Integral Panels
Press-braking bending is widely applied in the manufacture of aircraft integral panels because of the advantages of strong adaptability to different contours, simplicity of bending tools, short manufacturing time and low process cost. However, a simulation of bending process requires long-time calculation and consumes extensive computational resources. Considering the factors that the original model (ORM) of an integral panel is large and the press-braking bending is used only for the local area of integral panels with heavy thickness in practice, an equivalent calculation method for press-braking bending analysis of integral panels is proposed. The local bending area of an integral panel is simplified to a model of plate in this method. An exponential strengthening model is used to derive the equations of stress, strain and forming radius of the ORM and its simplified model (SPM). Meanwhile, the equivalent parameters of the SPM are determined and deduced based on three principles: that the material begin to be yielded simultaneously, the ultimate stress of the ORM is the same as that of the SPM at the same punch displacement, and the forming radii of neutral surfaces of the ORM and the SPM are identical after springback. The distribution of the stress and strain determined by finite element (FE) simulations are compared, and the FE simulations indicate that the contour curve of the SPM is in fairly good agreement with the profile of the ORM under the same bending process parameters, and the maximum difference is 13.17%. The computational efficiency is increased by more than 48%. Therefore, the proposed approach is quite suitable for industrial applications to improve the bending quality and efficiency of integral panels
Characteristics of Pesticide Residues and Dietary Exposure Risk Assessment on Commercial Grapes of Hubei Province in 2022
To investigate the residue characteristics of pesticides in commercial grapes in Hubei and their dietary exposure risk, 46 pesticide residues in 128 grape samples from large-scale local markets and supermarkets of Hubei Province in 2022 were analyzed by liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry. The dietary exposure of detected pesticides in grapes was assessed by the veterinary drug residues risk ranking matrix of the UK Veterinary Drug Residues Commission and the index of food safety (IFS). The results showed that the detection rate of the pesticide residue in grapes was 78.1%. Moreover, cyhalothrin detected in four samples exceeded the national maximum residue limit of pesticide and the exceeding rate was 3.1%. According to the residual risk score, there were 7 high-risk pesticides (avermectin, triazole alcohol and thiophanate-methyl, etc), 4 medium-risk pesticides (thiamethoxam, tebuconazole, acetamiprid and cypermethrin) and 9 low-risk pesticides (enoylmorpholine, azoxystrobin and imazalil, etc) among the pesticides detected. Based on the results of risk index, medium-risk samples accounted for 3.1%, and low-risk and very low-risk samples accounted for 96.9%. On the basis of the results of the food safety index method, the IFS values of 20 pesticides detected were lower than 1, indicating that the dietary exposure risk was within an acceptable range. In general, the grape samples monitored in this study had good safety characteristics and low health risks
The electron beam irradiation damage on nanomaterials synthesized by hydrothermal and thermal evaporation methods – An example of ZnS nanostructures
Using transmission electron microscopy-related techniques, we have compared the degradation behaviors of several different types of ZnS nanostructures, including the ZnS nanosheets synthesized by hydrothermal method (with different oxygen impurity concentration) and ZnS nanobelts grown using thermal evaporation. We have identified that displacement damage, sputtering, and oxidation mechanisms exist during the electron irradiation process. While oxidation of the nanostructure is always observed, displacement damage appears to be the dominant mechanism contributing to the final structural collapse of ZnS nanosheets (synthesized via hydrothermal methods), but sputtering mechanism becomes critical in changing the surface roughness of the ZnS nanobelts (grown by thermal evaporation). The specific damage mechanisms of these nanomaterials disclose that different synthesis process results in different structure quality (particularly impurity related interior defects) of the ZnS nanostructures, which determines their specific degradation behaviors under the electron beam irradiation. © 2010 Elsevier Ltd
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